Ultrasound heater-agitator for thermal tissue treatment

ABSTRACT

A device is for thermal treatment of tissue. The device includes (a) an elongated member extending from a proximal end to a distal end insertable to a target position within a body; (b) a housing coupled to the distal end of the elongated member sized and shaped for insertion to a target organ within a living body, the housing including an opening permitting fluid surrounding the housing to enter the housing, the housing further including first and second deflecting elements shaped to diffuse pulses of fluid directed thereagainst; and © a piezoelectric element mounted within the housing between the first and second deflecting elements. The piezoelectric element is oriented to generate pulses in liquid received within the housing toward the first and second deflecting elements.

PRIORITY CLAIM

This application is a which is Continuation application of U.S. patentapplication Ser. No. 12/748,964 filed on Mar. 29, 2010, now U.S. Pat.No. 8,287,472; which claims the priority to U.S. Provisional ApplicationSer. No. 61/174,225 on Apr. 30, 2009. All applications/patents areexpressly incorporated herein, in their entirety, by reference.

BACKGROUND

sound energy has been applied to tissue for various thermal treatmentsand has been used in mechanical actuators based on motion/deformation ofa piezoelectric element. Separately, heated fluids have been employed inthe thermal treatment of tissue such as ablation. For example, inhydrothermal ablation, fluid heated to approximately to 90° C. isintroduced into the uterus to ablate the lining thereof. To ensure eventemperature distribution, this fluid must be agitated and circulatedwithin the uterus via, for example, an external heater and pump. Thefluid is heated as it passes through the heater while being pumped in acycle into and out of the uterus. However, as this fluid circulates inand out of an organ such as the uterus, tissue particles in the fluidmay become lodged in the external heater or the pump reducing thecirculation of the fluid and the uniformity of the ablation of theendometrium.

SUMMARY OF THE INVENTION

The present invention is a method and a device to deliver heat andmechanical agitation to a liquid. More specifically, the presentinvention is directed to a method and device for thermal treatment oftissue within a living body, the device comprises a housing extendingfrom a distal end to a proximal end, the housing including a firstopening exposing an inner chamber of the device to the fluid, thehousing being sized and shaped for insertion to a target location withinthe body and a piezoelectric element fixed within the housing andgenerating pulses of ultrasound energy directed substantially along alongitudinal axis of the housing in combination with first and seconddeflecting elements, the first deflecting element being mounted withinthe housing on a distal side of the piezoelectric element, the seconddeflecting element being mounted within the housing on a proximal sideof the piezoelectric element, the first and second deflecting elementsdeflecting a portion of ultrasound energy from the piezoelectric elementaway from the axis of the housing so that the deflected ultrasoundenergy exits the housing via the first opening. In general, thisinvention reveals a method and device to deliver heat and agitation in aliquid using ultrasound.

The present invention is further directed to a method, comprisingimmersing a device in a fluid within a living body, the device includinga housing extending from a distal end to a proximal end and includingopenings exposing an inner chamber of the device to the fluid, apiezoelectric element mounted within the housing aligned so that, whenexcited, the piezoelectric element generates pulses of ultrasound energydirected substantially along a longitudinal axis of the housing andfirst and second deflecting elements, the first deflecting element beingmounted within the housing on a distal side of the piezoelectric elementand the second deflecting element being mounted within the housing on aproximal side of the piezoelectric element. The piezoelectric element isexcited to generate ultrasound energy of a desired frequency andamplitude directed toward the first and second deflecting elements sothat a portion of the ultrasound energy impinging on the first andsecond deflecting elements is deflected therefrom to target tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a device according to an exemplaryembodiment of the present invention;

FIG. 2 shows an enlarged perspective view of the device of FIG. 1;

FIG. 3 shows an enlarged perspective view of the device of FIG. 1 with aportion of a housing of the device removed;

FIG. 4 shows the device of FIG. 1 in which a piezoelectric elementgenerates ultrasound energy; and

FIG. 5 shows the device of FIG. 1 heating and agitating a fluid.

DETAILED DESCRIPTION

The present invention, which may be further understood with reference tothe following description and the appended drawings, relates to devicesfor thermal treatment of tissue. Exemplary embodiments of the presentinvention heat and/or agitate fluids within a living body (e.g., withina hollow organ) to treat tissue. One exemplary procedure that will bedescribed below is hydrothermal ablation of the lining of the uterus. Itshould be noted, however, that although the embodiments of the presentinvention are described in regard to the ablation of the endometrium,the invention is relevant to the use of an ultrasound device which heatsfluids within the body for any thermal treatment of tissue and may beemployed, for example, in organs such as the urinary bladder, thestomach, etc.

FIGS. 1-5 show a device 100 according to an exemplary embodiment of thepresent invention. As shown in FIG. 1, the device 100 may be connectedto an external power source 150 via a flexible elongate member 160. Thedevice 100 may be mounted on a distal end 162 of the elongate member 160while the power source 150 may be connected to a proximal end 164 suchthat the power source 150 may remain external to the body when thedevice 100 is inserted into the body. Once inserted, the device 100 maybe immersed in a fluid 170 within the body (e.g., within an organ suchas the uterus). As shown in FIG. 2, the device 100 may further comprisea piezoelectric element 102, a pair of deflecting elements 104, 106, ahousing 108 and a transmission line 110. The piezoelectric element 102and the deflecting elements 104, 106 between which the piezoelectricelement 102 is positioned are held in the housing 108 while thetransmission line 110 extends from the piezoelectric element 102 to theexternal power source 140 along or within the elongate member 160 totransmit power (e.g., RF energy) from the power source 150 to the device100.

As shown in FIG. 3, the piezoelectric element 102 may be formed as athin, substantially flat disc fixed within the housing 108 with firstand second surfaces 112, 114, respectively, thereof substantiallyexposed while an outer perimeter 116 thereof remains encased by thehousing 108. The piezoelectric element 102 may be manufactured of anyknown material exhibiting a piezoelectric effect such as, for example,crystals and ceramics. One such suitable material is PZT (i.e., leadzirconate titanate). As understood by those skilled in the art, thepiezoelectric effect generates mechanical stress in the material when anelectric potential is applied thereto. Thus, the first and secondsurfaces 112, 114 are metal-plated (e.g., silver, nickel and gold) suchthat an electric potential may be applied across the piezoelectricelement 102. The transmission line 110 may be formed, for example, as anelongated electrically conducting member a distal end 116 of which isattached to the piezoelectric element 102 while a proximal end 118thereof is accessible at a proximal end 122 of the device 100 forcoupling to an external source of electric energy 150. When pulsedelectrical energy is transferred to the piezoelectric element 102 viathe transmission line 110, the changes in electric potential appliedthereto cause the piezoelectric element 102 to vibrate, creatingpressure pulses adjacent to the first and second surfaces 112, 114.Ultrasound energy in the form of pulses in the fluid 170 moves away fromthe first and second surfaces 112, 114, substantially perpendicular tothose surfaces as shown in FIG. 3. As the piezoelectric element 102 ispositioned between the two deflecting elements 104, 106, the ultrasoundenergy is reflected out of the housing 108 from one of the deflectingelements 104, 106.

The deflecting elements 104, 106 are fixed to the housing 108 on eitherside of the piezoelectric element 102 with the distal surface 112 of thepiezoelectric element 102 facing a first one of the deflecting elements104 while the proximal surface 114 faces the second deflecting element106. The first deflecting element 104 is fixed at a distal end 120 ofthe housing 108 while the second deflecting element 106 is fixed at theproximal end 122 of the housing 108. The arrangement of thepiezoelectric element 102 within the housing 108 generating pulsesdirected substantially along the longitudinal axis thereof anddeflecting elements 104, 106 to diffuse and redirect this ultrasoundenergy out of the housing 108 prevents the bulk of the ultrasound energyfrom directly impacting and burning the tissues of the uterus. Thedeflecting elements 104, 106 are preferably shaped such that theultrasound energy from the piezoelectric element 102 is not directlyreflected therefrom but is scattered to distribute the energy over awider tissue surface area. For example, a surface 124 of the deflectingelement 104 and a surface 126 of the deflecting element 106 may besubstantially spherically convex such that the pulses of ultrasoundenergy are dispersed upon reflection therefrom. Each of the surfaces124, 126 may also include a plurality of protrusions 128, 130,respectively, which roughen the surfaces 124, 126 to further scatter theultrasound energy in various directions. To deflect the ultrasoundenergy in a directional stream for better heat transfer and distributionto a desired target area, the surfaces 124, 126 may be angled withrespect to a plane of the piezoelectric element 102. In a preferredembodiment, the surface 124 may be angled in a direction opposite thatof the surface 126 such that pulses of ultrasound energy which contactthese angled surfaces 124, 126 are scattered in opposite directions toform a generally circulatory pattern of fluid flow. Thus, the surface124 agitates the fluid 170, causing it to circulate through the organwithout being overwhelmingly directed to a single spot which wouldotherwise be burned.

If desired, the deflecting elements 104, 106 may be formed to absorb aportion of the ultrasound energy and convert it to heat to heat thesurrounding fluid 170. The deflecting elements 104, 106 may be formed ofa thermally conductive ceramic, such as Aluminum Silicone Carbride,which is manufactured by CPS Technologies Corporation (Norton, Mass.). Athermally conductive material allows for quick heat dissipation. Foroptimal coupling of the ultrasound energy, an acoustic impedance of theceramic should match the acoustic impedance of the fluid 170. It will beunderstood by those of skill in the art that the closer the two valuesare to one another, the more acoustic energy the deflecting elements 104will absorb. For example, the acoustic impedance of ceramic,Z_(ceramics)=˜36 Mrayls, while the acoustic impedance of a fluid 170such as water is Z_(water)=1.5 Mrayls. Because of the substantialdifference in acoustic impedance values, the deflecting element 104 willhave difficulty coupling the ultrasound energy. However, any ultrasoundenergy that is coupled from the fluid into the deflectors, would bequickly converted into heat which would then be conducted into thefluid. A significant portion of the ultrasound energy impinging on thedeflecting elements 104, 106 will be reflected from the deflectingelements 104, 106 because of the difference in acoustic impedancebetween the water and the material of the deflecting elements 104, 106.Thus, a desired ratio of ultrasound energy reflected from the deflectingelements 104, 106 to energy coupled and absorbed thereby, may beachieved by selecting a composition of the deflecting elements 104, 106to have an acoustic impedance which differs from that of the fluid 170by an amount corresponding to the desired ratio.

So that the deflecting elements 104, 106 may better couple theultrasound energy, the surfaces 124, 126 thereof may be coated with athin layer of thermally conductive UV cured epoxy, filled with ceramicpowder. One example of such an epoxy is manufactured by DymaxCorporation (Torrington, Conn.). The acoustic impedance of this UV curedepoxy layer is Z_(layer)=˜5-7 Mrayls, which would make the acousticimpedance of the deflecting elements 104, 106 very close in value to theacoustic impedance of water since the acoustic impedance of the perfectmatching layer would be calculated asZ_(layer)=√(Z_(water)XZ_(ceramics))=√(1.5×36)=7.3 Mrayls. For thisparticular Dymax manufactured UV cured epoxy layer, the thickness of thelayer may be a multiple of an odd number of quarter wavelengths (i.e.,(2n+1)×¼λ). The wavelength, λ is a function of a sound velocity in thematerial V and frequency F of the piezoelectric element vibration withλ=V/F. For example, if the velocity of sound in the ceramic filled epoxyis V=2×10⁶ mm/sec and the frequency of excitation of the piezoelectricelement is F=16 MHz=16×10⁶ cycles/sec, then λ=(2×10⁶ mm/sec)/(16×10⁶cycles/sec)=0.125 mm. This wavelength may be used to determine a desiredthickness of the matching layer. It will be understood by those of skillin the art that various matching layers and frequencies may be useddepending on the fluid 170 within which the piezoelectric element 102will be immersed and on the material of the piezoelectric element 102.It will also be understood by those of skill in the art that higher thefrequencies allows for faster absorption of the ultrasound energy by thefluid 170 and the deflecting elements 104, 106. In a preferredembodiment, the frequency may range from 5-100 MHz.

In another embodiment, the deflecting elements 104, 106 may be formed ofa highly porous hydrophilic ceramic. An example of such a material ismanufactured by Soilmoisture Equipment Corporation (Santa Barbara,Calif.). The open pore structure of the material provides a convolutedpath of interconnecting networking channels, allowing a complete flowthroughout the material for migrating fluid 170. This allows efficientcoupling of the mechanical energy from the fluid 170 into the deflectingelements 104, 106 and conversion of the energy into heat within thedeflecting elements 104, 106. It will be understood by those of skill inthe art that a variety of porous materials may be selected for thedeflecting elements 104, 106 depending on an appropriate pore size andvoid volume, which would be selected for optimal performance.

As would be understood by those skilled in the art, the device 100 mayinclude a flexible insertion section similar to those of endoscopes andother minimally invasive surgical instruments with the housing 108mounted at a distal end thereof. For such a device 100, the housing 108which encases the piezoelectric element 102 and the deflecting elements104, 106 will be sized and shaped such that the device 100 may beinserted into the body via a naturally occurring bodily orifice andadvanced through a body lumen to a target site therein or to anextralumenal target site. The housing 108 may be a substantiallylongitudinal and hollow member extending from the distal end 120 to theproximal end 122. The distal and proximal ends 120, 122 may be open suchthat the deflecting elements 104, 106, fixed within the housing 108 atthese ends 120, 122 are exposed. The housing 108 may also includecut-outs 132, 134, 136, 138 through a surface 140 of the housing 108 tofacilitate the transfer of energy from the piezoelectric element 102 tothe surrounding area. The cut-outs 132, 134, 136, 138 may cover asubstantial surface area of the housing 108 such that the first andsecond surfaces 112, 114 and the surfaces 124, 126 of the deflectingelements 104, 106 are substantially exposed to the outside of the device100. The cut-outs 132, 134, 136, 138 allow ultrasound energy in the formof pulses of fluid to easily pass through the device 100 such that thesurrounding fluid 170 may be heated and agitated thereby. It will beunderstood by those of skill in the art that although the device 100 isshown in FIGS. 1-5 as including four cut-outs, the housing 108 mayinclude any number of cut-outs so long as an interior of the housing 108is exposed to the exterior of the device 100 such that ultrasound energymay easily pass therethrough.

The fluid 170 may be water, as described above, saline, or another otherfluid appropriate for hydrothermal ablation or any other thermaltreatment utilizing heated fluid 170. The fluid 170 may be supplied tothe uterus, or any other treatment site via a catheter or other fluidsupply tool as would be understood by those skilled in the art. Afterthe fluid 170 has been supplied to the treatment site, the device 100may be inserted into the organ via a naturally occurring orifice in thebody or via any other opening (e.g., a surgical incision). Once at thetreatment site, the device 100 is immersed in the fluid 170 and RFenergy is delivered to the piezoelectric element 102. As describedabove, the RF energy excites and vibrates the piezoelectric element 102generating ultrasound energy in the form of pulses of fluid pressuremoving away from the first and second surfaces 112, 114 toward thedeflecting elements 104, 106 as shown in FIG. 4. This ultrasound energyis depicted by the directional arrows in FIG. 4. The pulses of energymove substantially perpendicularly to the piezoelectric element 102, toimpinge on the surfaces 124, 126 of the deflecting elements 104, 106which face the piezoelectric element 102.

Some of the beams of energy that hit the piezoelectric element 102 willbe absorbed by the deflecting elements 104, 106 while some of the energywill be deflected by the angled surfaces 124, 126 of the deflectingelements 104 setting up a substantially circular fluid motion, asdepicted in FIG. 5. The angles of the surfaces 124, 126 ensure thatfluid pulses leaving the surfaces 124, 126 exit the housing 108 via thecutout 132, 134, 136, 138 shown in FIG. 2. In a preferred embodiment,the surfaces 124, 126 are positioned at opposite angles relative to oneanother such energy is deflected from these surfaces in oppositedirections—i.e., diametrically opposed relative to a longitudinal axisof the housing 108. For example, energy leaving the first surface 112 ofthe piezoelectric element 102 deflected from the surface 124 of thedeflecting element 104 exits the housing 108 via the cut-out 132. Aportion of the energy deflecting off tissue (e.g., a wall of a bodycavity within which the device 100 is located) may re-enter the housing108 via cut-out 134. Likewise, energy leaving the second surface 114 ofthe piezoelectric element 102 deflected from the surface 126 of thedeflecting element 106 exits the housing 108 via the cut-out 136. Aportion of the energy deflecting off of the tissue may re-enter thehousing 108 via cut-out 138. Thus, the beams of energy are able tocreate a substantially circular pattern of motion.

Additionally, the spherically convex shape of the surfaces 124, 126,along with the protrusions 128, 130, scatter the ultrasound beams. Thescattering also aids to de-focus the ultrasound beams such that thebeams lacks the intensity necessary to produce a burn when it enters thetissue. An amount of energy that is absorbed by the deflecting elements104, 106 will be dependent upon the acoustic impedance of both the fluidand the deflecting elements 104, 106. The energy and fluid 170 that isabsorbed by the deflecting elements 104, 106 are converted to heat suchthat the surrounding fluid 170, or the fluid 170 within the deflectingelements 104, 106 if the material is highly porous, may be heated. Asthe deflecting elements 104, 106 also keeps the fluid 170 movingcircularly through the organ, the heated fluid 170 is agitated anddistributed evenly through the organ.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the structure and themethodology of the present invention, without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover modifications and variations of the invention providedthat they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A device for thermal treatment of tissue,comprising: an elongated member extending from a proximal end to adistal end insertable to a target position within a body; a housingcoupled to the distal end of the elongated member sized and shaped forinsertion to a target organ within a living body, the housing includingan opening permitting fluid surrounding the housing to enter thehousing, the housing further including first and second deflectingelements mounted therein and shaped to diffuse pulses of fluid directedthereagainst; and a piezoelectric element mounted within the housingbetween the first and second deflecting elements, the piezoelectricelement being oriented to generate pulses in liquid received within thehousing toward the first and second deflecting elements.
 2. The deviceof claim 1, further comprising a transmission line connecting thepiezoelectric element to an external power source.
 3. The device ofclaim 1, wherein the piezoelectric element is a flat disc.
 4. The deviceof claim 3, wherein the first and second deflecting elements are mountedon proximal and distal ends of the housing, respectively, each of thefirst and second deflecting elements facing a corresponding side of theflat disc of the piezoelectric element.
 5. The device of claim 1,wherein deflecting surfaces of the first and second deflecting elementsare convex.
 6. The device of claim 1, wherein a deflecting surface ofthe first deflecting element facing the piezoelectric element includes afirst protrusion to scatter fluid pulses from the piezoelectric element.7. The device of claim 3, wherein the piezoelectric element extends in aplane perpendicular to a longitudinal axis of the housing, a deflectingsurface of the first deflecting element facing the piezoelectric elementbeing angled with respect to the plane of the piezoelectric element todeflect fluid pulses therefrom away from the longitudinal axis of thehousing.
 8. The device of claim 7, wherein a deflecting surface of thesecond deflecting element facing a side of the piezoelectric elementopposite the side faced by the first deflecting element is angled withrespect to the plane of the piezoelectric element to deflect pulses offluid from the piezoelectric element away from the longitudinal axis ofthe housing in a direction different from the pulses deflected by thefirst deflecting element.
 9. The device of claim 1, wherein each of thefirst and second deflecting elements is formed of one of a thermallyconductive material allowing for rapid heat dissipation and a highlyporous hydrophilic material.
 10. The device of claim 1, whereindeflecting surfaces of the first and second deflecting elements arecoated with a thin layer of material having an acoustic impedancematching an acoustic impedance of water.
 11. The device of claim 1,wherein the housing is an elongated hollow member having an openproximal end closed by the first deflecting element and an open distalend closed by the second deflecting element.
 12. The device of claim 10,wherein the housing comprises a plurality of cutouts facilitating atransfer of ultrasound energy from the piezoelectric element to asurrounding area.
 13. The device of claim 1, wherein the piezoelectricelement produces ultrasound energy in the form of pulses traveling alongan axis perpendicular to a plane of the piezoelectric element.
 14. Adevice for supplying ultrasound energy, comprising: a housing sized andshaped for insertion to a target organ within a living body, the housingincluding an opening permitting fluid surrounding the housing to enterthe housing, the housing further including first and second deflectingelements mounted therein and shaped to diffuse pulses of fluid directedthereagainst; and a piezoelectric element mounted within the housingbetween the first and second deflecting elements, the piezoelectricelement being oriented to generate pulses in liquid received within thehousing toward the first and second deflecting elements.
 15. The deviceof claim 14, wherein the piezoelectric element extends in a planeperpendicular to a longitudinal axis of the housing and producesultrasound energy in the form of pulses traveling along an axisperpendicular to a plane of the piezoelectric element.
 16. The device ofclaim 15, wherein the piezoelectric element extends in a planeperpendicular to a longitudinal axis of the housing, a deflectingsurface of the first deflecting element facing the piezoelectric elementbeing angled with respect to the plane of the piezoelectric element todeflect fluid pulses therefrom away from the longitudinal axis of thehousing and a deflecting surface of the second deflecting element facinga side of the piezoelectric element opposite the side faced by the firstdeflecting element is angled with respect to the plane of thepiezoelectric element to deflect pulses of fluid from the piezoelectricelement away from the longitudinal axis of the housing in a directiondifferent from the pulses deflected by the first deflecting element. 17.The device of claim 14, wherein the first and second deflecting elementsare mounted on proximal and distal ends of the housing, respectively,each of the first and second deflecting elements facing a correspondingside of a flat disc of the piezoelectric element.
 18. The device ofclaim 14, wherein deflecting surfaces of the first and second deflectingelements are convex.
 19. The device of claim 14, wherein a deflectingsurface of the first deflecting element facing the piezoelectric elementincludes a first protrusion to scatter fluid pulses from thepiezoelectric element.
 20. A system for thermal treatment of tissue,comprising: an elongated member extending from a proximal end to adistal end insertable to a target position within a body; a housingcoupled to the distal end of the elongated member sized and shaped forinsertion to a target organ within a living body, the housing includingan opening permitting fluid surrounding the housing to enter thehousing, the housing further including first and second deflectingelements mounted therein and shaped to diffuse pulses of fluid directedthereagainst; a piezoelectric element mounted within the housing betweenthe first and second deflecting elements, the piezoelectric elementbeing oriented to generate pulses in liquid received within the housingtoward the first and second deflecting elements; and a power sourceconnected to the proximal end of the elongated member and supplyingpower to the piezoelectric element.